Download ppt

Nematode Sinusoidal Movement
Major muscles are down dorsal and ventral sides.
Contraction makes nematodes slide on their sides.
Pushing force must exceed adhering force.
Movement of nematodes in different
thicknesses of water film
Peristaltic movement of Criconemoides curvatum
Rear end contracts
Wave of contraction passes forward, pushes head forward
Opposite of earthworm
Backward-directed
annules resist slipping
backward
Structure of the Stoma Relative to Feeding
Nematodes eat living organisms or their tissues
Feeding Behaviors
Holophagic = bacteria, algae,
yeasts, protozoa (A)
Fluid-feeders = stylet pierces
algae, plants, small fauna;
sucks out contents (B, C, D)
Predators capture prey and
swallow whole or in parts (E)
Animal parasites = primarily
blood feeders (F, G, H)
Stoma structure infers
trophic position!
Ingestion by Holophagic Feeding
A - Contractions open lumen, negative pressure sucks in particles
B - Muscles relax, lumen narrows, water goes back out mouth
C - Wave of contractions move food particles into intestine
Variations in Holophagic Feeding
A - Panagrellus
B - Ascaris
C - Aplectana
Pumping rate = 1-5/sec, bursts = 20/sec
Nematode Esophageal Types
Kathy Merrifield
K. Merrifield
www.fcps.k12.va.us
J.D. Eisenback
Nemapix 1
Some nematodes pierce the cuticle of prey
with a stylet, inject enzymes and ingest
the internal body fluids. (Seinura sp.)
Fluid-Feeding
Predators
Fluid-Feeding
Fungal Feeders
Fluid-Feeding
Plant Feeders
Scott Edwards
U. Wyss
Fluid-Feeding
Plant Feeders
Locating Host
Exploration = find roots by chance
Attraction = respond to gradients in:
CO2
exudates
rhizosphere microbial products
Attraction may reach ½ meter
> mile in human scale
U. Zunke
Fluid-Feeding
Plant Feeders
Locating Feeding Site
- Exploration of root = probe w/o puncturing
- Head rocks side to side, papillae touch root
- Arches body to bring stylet at right angles
to root for maximum thrust
- Polysaccharide plug may glue
lips to root
Fluid-Feeding
Plant Feeders
Stylet Penetration
-Nematode penetrates cell wall with stylet
-Only part of stylet used so many thrusts
required, up to 2-6 thrusts/sec
-Nematode may move head back and forth
-Show film clip
Fluid-Feeding
Plant Feeders
Ingestion
-Pause after stylet penetration (1)
-Enzymes may be secreated into
cell for predigestion (2),
20 sec-2 hrs, cyclosis may stop
-Median bulb pumps cell contents
into esophagus (3)
-Turgor pressure in cell may assist
-Cell may collapse (4)
-Feeding time/cell 1-5 min to 1 wk
Fluid-Feeding
Plant Feeders
Ingestion
-In other cases cyclosis may continue while
cell is fed upon
-Cell not damaged
Fluid-Feeding
Plant Parasites - Invasion
Migratory ectoparasites – withdraw stylet, move to
new cell, & repeat process
Endoparasites – penetrate further into tissues
Root-knot J2 collect behind apical meristem,
perforate epidermal cell with stylet until cell wall
collapses, push head inside = 3-24 hrs
High populations = competition for invasion sites.
J2 may follow in the same hole, enlarging it and the
hole may become surrounded by necrotic cells.
Fluid-Feeding
Plant Parasites - Invasion
W. Wergi
Fluid-Feeding
Plant Parasites - Invasion
Enter through natural openings
-Lenticels in potato tubers
-Junctions between primary and lateral roots
-Stomata in leaves
Fluid-Feeding
Plant Parasites - Tunneling
-“Cut” holes through cell walls with stylet
- Force between cells = “unzip” middle lamella
(Root-knot, Meloidogyne)
- Digest holes through cell walls with enzymes
(Burrowing nematode, Radopholus similis)
Fluid-Feeding
Plant Parasites - Tunneling
Movement through the root is periodic as the
nematode occasionally stops to feed.
D. Wixted
Fluid-Feeding
Plant Parasites - Feeding
Endoparasites disrupt tissues
during feeding
Enzymes secreted = tissues
enlarge, separate & collapse to
form cavities (D)
Specialized feeding cells are
formed
(E) = nurse cells
(F) = giant cells
Animal Parasites
Discuss Later
Nematode Reproduction
“Sex of an individual depends on gamete produced”
Sperm = male
Eggs = female
Both = hermaphrodite
Eggs
embryo w/o sperm = parthenogenic female
Nematodes are extremely varied in their
patterns of reproduction.
Nematode Reproduction
Amphimixis = eggs and sperm come from
separate individuals during cross fertilization
where male deposits sperm in reproductive
tract of female. Most common type
Males with a bursa align “parallel” to female
Males without bursae align “perpendicular”
to the female's body and the entire posterior
region folds over and grasps the vulva.
“Cement” may hold nematodes together.
Nematode Reproduction
Amphimixis
Sex attractants aid males and females to find
each other.
Sedentary = only females produce
Migratory = both sexes produce & respond
Nematode Reproduction
Under normal conditions, most amphimictic
populations maintain a 1:1 sex ratio.
Stress in environment can alter the sex ratio.
Usually the response is to inadequate nutrition.
Developing population = predominantly male.
Differential survival, more female mortality.
High temperatures, increased CO2 and
accumulation of certain chemicals may also
increase the ratio of males to females.
Nematode Reproduction
Automixis = self fertilization by hermaphrodites
Egg and sperm come from same individual
Syngonic hermaphrodites = eggs and sperm
produced in the “same gonad” ovotestis.
Sperm produced first, stored while eggs are
produced. Fertilized as move towards uterus.
Diagonic hermaphrodites have “separate
structures” for producing eggs and sperm.
Different gametes produced at same time.
Nematode Reproduction
Pseudomixis (pseudogamy)
Participation of male gamete necessary for
oocyte development but no fertilization.
Facultative pseudogamy = unfertilized eggs
become males, fertilized eggs become females.
Redundant pseudogamy = sperm is deposited
in reproductive tract but doesn't penetrate egg.
Nematode Reproduction
Parthenogenesis = “females beget females”
Reproduction from unfertilized eggs without
participation of a male gamete.
Mitotic parthenogenesis = Retains the somatic
number of chromosomes = no pairing of
homologous chromosomes during prophase.
Oocytes remain diploid.
(n  2n without cell division
= mitosis without cytokinesis)
Nematode Reproduction
Parthenogenesis = “females beget females”
Meiotic parthenogenesis = two maturation
divisions = Results in eggs that are haploid.
Diploid condition restored by fusion of egg
nucleus with nucleus of nonextruded polar body.
Facultative meiotic parthenogenesis occurs in
noninseminated females or non-fertilized eggs.
Fertilized eggs = amphimictic development.
Both processes can occur in same female.
Nematode Reproduction
Nematode Reproduction
Oviparous = eggs released
Ovoviviparous = living young released
Endotokia matricida = eggs hatch in uterus,
juveniles burrow through the uterus into the
body cavity and feed on body of the mother.
Nematode Reproduction
Migratory nematodes eggs move down the
ovary into the uterus and are laid one at a time
as soon as they reach the vulva.
Sedentary parasites eggs are in a cluster either
outside (root-knot) or inside (cyst) the body.
Most nematodes lay eggs in the soil but
endoparasites lay eggs in the soil or inside
plant tissues.
Juveniles develop within egg,
may go through one or two
molts before hatching.
Most hatch spontaneously as
soon as they reach the end of
embryonic development.
Temperature and moisture
regulate developmental time.
Some plant parasites need
stimulus such as elevated
CO2, or root exudate to
trigger hatching sequence.
Some species require diapause
During the hatching process, either the shell is
softened by enzymes, or the nematode uses its stylet
to puncture a hole in the shell.